Chronos in Aristotle’s Physics: On the Nature of Time is a contribution both to Aristotle studies and to the philosophy of nature and speaks to the resurgence of interest in Aristotle’s natural philosophy. It argues that Aristotle’s Treatise on Time (Physics iv 10-14) is a highly contextualized account of time, not a treatment of time qua time but a parallel account to Aristotle’s foregoing studies of nature, principles (192b13-22), motion (201a10-11), infinite (iii 4-8), place (iv 1-5), and void (iv 6-9) in the Physics i-iv 9. It offers a reading of Physics iv 10-11 with the aim of showing that time, chrόnos, here has to do with time as an attribute of motion, as an interval, i.e., the type of time that, as Aristotle describes at 218a1, “is taken.” With support from a reading of Physics iv 14 and evidence from Aristotle’s greater philosophy of nature, it argues that time for Aristotle is derivative of the modal change of natural being. Time is then only ever potentially actual unless this change is apprehended, in most cases, by the working together of perception and intellection and, in some cases, by perception alone. Studies in contemporary animal science help to buttress this final conclusion.